1. Field of the Invention
The invention relates to the removal of the fines from the oil shale bed on a travelling grate retort.
2. Prior Art
Oil bearing shale may be retorted to recover shale oil by processing the shale in a retort. Among the variety of retorts known in the art, travelling grate retorts, both circular and straight have gained prominence in oil shale retorting technology. In order to obtain the optimum quality shale oil from any retort, it is necessary to reduce the particulate content of the oil to as low a level as is possible. Additionally, to maximize the retorting rate, the oil bearing shale should be as permeable as possible.
Typically, oil bearing shale is pre-sized prior to being placed on the retort, with the majority of the fine particles removed by screening. Due to the inherent limitations in screening techniques, some fine particles cling to and are mixed with the shale particles as the shale is charged onto the travelling grate. The oil shale bed on the travelling grate retort is quiescent during the process, with the oil bearing shale being transported through the various drying, heating, retorting, combustion, heat recovery and cooling zones as required on the travelling grate. The retorting process is driven by a perpendicular cross-flow of process gas or air as required for the particular function being performed. The cross-flow of process gas and/or air may entrain the remaining fine particles from the oil shale bed on the travelling grate. These entrained solids can then be deposited as contaminants in the collected shale oil. Post-retorting treatment is presently required to remove the solid particulate contaminants from the shale oil.
It is an object of this invention to remove the fines from the oil shale bed on a travelling grate retort prior to the actual retorting of the oil bearing shale so that the oil will not be contaminated with the particulate solids.
It is a further object of the invention to increase the permeability of the oil shale bed which will in turn, result in an increase in the rate of oil shale processing.